BT allows its red teams to attack live systems without informing the rest of the business or the blue team defending it. The companys defense-in-depth strategy internally is called Cytadel. The strategy is based on the idea that traditional citadels are surrounded by walls, ditches, high areas, ground surveillance and moats. If a single element fails, levels of protection are in place. If that one brick wall fails, everything falls, so this is about frustrating, and denying, and delaying bad things happening.”]
Source: https://www.csoonline.com/article/3481604/why-bts-red-team-strikes-for-real.html